Amorphous carbon films are used in patterning and as etch stop layers in semiconductor processing. As an etch stop layer, they are also known as ashable hard masks (AHMs). Etch selectivity of AHM is influenced primarily by the incorporated concentration of hydrogen. Reducing the amount of hydrogen incorporated in the film drives down the etch rate of the hard mask, thus increasing the selectivity.
To date, known methods of producing AHM with low hydrogen (H) content (e.g., below 20%) rely on a relatively high temperature (greater than 500° C.) PECVD deposition process. Many PECVD reactors are not designed to withstand such high processing temperatures, however. At process temperatures of about 400° C. and below, films typically have a high hydrogen content (about 40%) and corresponding relatively low etch selectivity. Accordingly, it would be desirable to be able to produce a hard mask film with a low hydrogen content (e.g., less than 30%, or 20%) and high etch selectivity at a relatively low deposition temperature (below 500° C., e.g., no more than 400° C.).